Coating compositions for packaging articles such as food and beverage containers

ABSTRACT

An article, comprising a food or beverage container, or a portion thereof, that includes a metal substrate and a coating disposed on at least a portion of the metal substrate. The coating is preferably formed from a coating composition that comprises a latex emulsion having a first-stage emulsion polymerized copolymer and a second-stage emulsion polymerized copolymer.

CROSS REFERENCE TO RELATED MATTERS

This application is a continuation of U.S. patent application Ser. No.14/902,546, filed Jul. 1, 2014, which is a national stage entry under 35U.S.C. § 371 of PCT Application No. PCT/US2014/045067, filed Jul. 1,2014, which claims the benefit of U.S. Provisional Application No.61/842,044, filed Jul. 2, 2013. The entire contents of each of which areincorporated herein by reference.

FIELD

The present disclosure is directed to coating compositions. Inparticular, the present disclosure is directed to latex emulsion coatingcompositions, such as for forming coatings for food and beveragecontainers, as well as other packaging articles.

BACKGROUND

A wide variety of coatings have been used to coat the surfaces ofpackaging articles (e.g., food and beverage cans). For example, metalcans are sometimes coated using “coil coating” or “sheet coating”operations, i.e., a planar coil or sheet of a suitable substrate (e.g.,steel or aluminum metal) is coated with a suitable composition andhardened (e.g., cured). The coated substrate then is formed into the canend or body. Alternatively, liquid coating compositions may be applied(e.g., by spraying, dipping, rolling, etc.) to the formed or partiallyformed article and then hardened (e.g., cured).

Packaging coatings should preferably be capable of high-speedapplication to the substrate and provide the necessary properties whenhardened to perform in this demanding end use. For example, the coatingshould be safe for food contact, have excellent adhesion to thesubstrate, and resist degradation over long periods of time, even whenexposed to harsh environments.

Many current packaging coatings contain mobile or bound bisphenol A(“BPA”) or aromatic glycidyl ether compounds or PVC compounds. Althoughthe balance of scientific evidence available to date indicates that thesmall trace amounts of these compounds that might be released fromexisting coatings does not pose any health risks to humans, thesecompounds are nevertheless perceived by some people as being potentiallyharmful to human health. From the foregoing, it will be appreciated thatwhat is needed in the art is a packaging container (e.g., a food orbeverage can) that is coated with a composition that does not containextractible quantities of such compounds.

SUMMARY

An aspect of the present disclosure is directed to an article,comprising a packaging article such as a food or beverage container, ora portion thereof. The article includes a substrate, more preferably ametal substrate, and a coating disposed on at least a portion of thesubstrate. The coating is formed from a coating composition having alatex emulsion that is a reaction product of a method. The methodpreferably includes emulsion polymerizing first-stage monomers in anaqueous carrier to produce a first-stage copolymer having a highmolecular weight (e.g., a number-average molecular weight greater thanabout 50,000). The first-stage monomers preferably include at least 3%by weight of and comprising step-growth-functional monomers havingstep-growth-functional groups, based on an entire weight of thefirst-stage monomers groups. The method also includes emulsionpolymerizing a plurality of second-stage monomers in the presence of thefirst-stage copolymer to form a second-stage copolymer, where thesecond-stage copolymer includes a curing group configured to react withone of the step-growth-functional groups of the first-stage copolymerduring a curing step. Preferably, the coating composition issubstantially free of one or more of structural units derived from(meth)acrylamide-type monomers and bisphenol A.

Another aspect of the present disclosure is directed to a method ofmaking an inside spray coating composition for use with food or beveragecontainers. The method includes emulsion polymerizing first-stagemonomers including one or more polymerizable surfactant monomers in anaqueous carrier to produce a first-stage copolymer having a highmolecular weight (e.g., a number-average molecular weight greater thanabout 50,000), and where the first-stage copolymer includeswater-dispersing groups. The method also includes emulsion polymerizingsecond-stage monomers in the presence of the first-stage copolymer toform a second-stage copolymer, where the second-stage copolymer includesa curing group configured to react with the first-stage copolymer duringa curing step. The method also preferably includes formulating thecoating composition to provide a viscosity for a spray-coatingapplication.

Another aspect of the present disclosure is directed to a method offorming a coating on a food or beverage container, or portion thereof.The method includes providing a coating composition having an emulsionpolymerized latex, where at least a portion of the latex includes afirst-stage emulsion polymerized latex copolymer comprising at least 3%by weight of monomer units having step-growth-functional group, and asecond-stage emulsion polymerized latex copolymer comprising curinggroups (e.g., oxirane groups). The method also includes spraying theprovided coating composition onto an interior surface of the food orbeverage container, and heating the sprayed coating composition to curethe coating composition, thereby providing the coating on the interiorsurface of the food or beverage container.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the present disclosure.

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

As used herein, the term “organic group” means a hydrocarbon group (withoptional elements other than carbon and hydrogen, such as oxygen,nitrogen, sulfur, and silicon) that is classified as an aliphatic group,a cyclic group, or combination of aliphatic and cyclic groups (e.g.,alkaryl and aralkyl groups). The term “cyclic group” means a closed ringhydrocarbon group that is classified as an alicyclic group or anaromatic group, both of which can include heteroatoms. The term“alicyclic group” means a cyclic hydrocarbon group having propertiesresembling those of aliphatic groups.

The term “aryl group” (e.g., an arylene group) refers to a closedaromatic ring or ring system such as phenylene, naphthylene,biphenylene, fluorenylene, and indenyl, as well as heteroarylene groups(i.e., a closed aromatic or aromatic-like ring hydrocarbon or ringsystem in which one or more of the atoms in the ring is an element otherthan carbon (e.g., nitrogen, oxygen, sulfur, etc.)). Suitable heteroarylgroups include furyl, thienyl, pyridyl, quinolinyl, isoquinolinyl,indolyl, isoindolyl, triazolyl, pyrrolyl, tetrazolyl, imidazolyl,pyrazolyl, oxazolyl, thiazolyl, benzofuranyl, benzothiophenyl,carbazolyl, benzoxazolyl, pyrimidinyl, benzimidazolyl, quinoxalinyl,benzothiazolyl, naphthyridinyl, isoxazolyl, isothiazolyl, purinyl,quinazolinyl, pyrazinyl, 1-oxidopyridyl, pyridazinyl, triazinyl,tetrazinyl, oxadiazolyl, thiadiazolyl, and so on. When such groups aredivalent, they are typically referred to as “arylene” or “heteroarylene”groups (e.g., furylene, pyridylene, etc.).

A group that may be the same or different is referred to as being“independently” something.

Substitution is anticipated on the organic groups of the compounds ofthe present invention. As a means of simplifying the discussion andrecitation of certain terminology used throughout this application, theterms “group” and “moiety” are used to differentiate between chemicalspecies that allow for substitution or that may be substituted and thosethat do not allow or may not be so substituted. Thus, when the term“group” is used to describe a chemical substituent, the describedchemical material includes the unsubstituted group and that group withO, N, Si, or S atoms, for example, in the chain (as in an alkoxy group)as well as carbonyl groups or other conventional substitution. Where theterm “moiety” is used to describe a chemical compound or substituent,only an unsubstituted chemical material is intended to be included. Forexample, the phrase “alkyl group” is intended to include not only pureopen chain saturated hydrocarbon alkyl substituents, such as methyl,ethyl, propyl, t-butyl, and the like, but also alkyl substituentsbearing further substituents known in the art, such as hydroxy, alkoxy,alkylsulfonyl, halogen atoms, cyano, nitro, amino, carboxyl, etc. Thus,“alkyl group” includes ether groups, haloalkyls, nitroalkyls,carboxyalkyls, hydroxyalkyls, sulfoalkyls, etc. On the other hand, thephrase “alkyl moiety” is limited to the inclusion of only pure openchain saturated hydrocarbon alkyl substituents, such as methyl, ethyl,propyl, t-butyl, and the like. As used herein, the term “group” isintended to be a recitation of both the particular moiety, as well as arecitation of the broader class of substituted and unsubstitutedstructures that includes the moiety.

The terms “a”, “an”, “the”, “at least one,” and “one or more” are usedinterchangeably. Thus, for example, reference to “a” chemical compoundrefers one or more molecules of the chemical compound, rather than beinglimited to a single molecule of the chemical compound. Furthermore, theone or more molecules may or may not be identical, so long as they fallunder the category of the chemical compound. Thus, for example, “a”polyester is interpreted to include one or more polymer molecules of thepolyester, where the polymer molecules may or may not be identical(e.g., different molecular weights, isomers, etc. . . . ).

The term “substantially free” of a particular compound means that thecompositions of the present disclosure contain less than 100 parts permillion (ppm) of the recited compound. The term “essentially free” of aparticular compound means that the compositions of the presentdisclosure contain less than 10 ppm of the recited compound. The term“essentially completely free” of a particular compound means that thecompositions of the present disclosure contain less than 1 ppm of therecited compound. The term “completely free” of a particular compoundmeans that the compositions of the present disclosure contain less than20 parts per billion (ppb) of the recited compound.

The term “food-contact surface” refers to the substrate surface of acontainer (typically an inner surface of a food or beverage container)that is in contact with, or intended for contact with, a food orbeverage product. By way of example, an interior surface of a metalsubstrate of a food or beverage container, or a portion thereof, is afood-contact surface even if the interior metal surface is coated with apolymeric coating composition.

The term “on,” when used in the context of a coating applied on asurface or substrate, includes both coatings applied directly orindirectly to the surface or substrate. Thus, for example, a coatingapplied to a primer layer overlying a substrate constitutes a coatingapplied on the substrate.

Unless otherwise indicated, the term “polymer” includes bothhomopolymers and copolymers (e.g., polymers of two or more differentmonomers). Similarly, unless otherwise indicated, the use of a termdesignating a polymer class such as, for example, “acrylic” is intendedto include both homopolymers and copolymers (e.g., polyester-acryliccopolymers).

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.). Furthermore, disclosure of a range includesdisclosure of all subranges included within the broader range (e.g., 1to 5 discloses 1 to 4, 1.5 to 4.5, 1 to 2, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a two-piece food or beveragecontainer having a coating formed from the coating composition of thepresent disclosure.

FIG. 2 is a front view of an example spray coating process for sprayingthe coating composition of the present disclosure onto an interiorsurface of a can, such as a food or beverage can.

FIG. 3 is a top view of the example spray coating process shown in FIG.2.

DETAILED DESCRIPTION

The present disclosure is directed to a latex copolymer, and a relatedcoating composition for use in forming products, such as coatings onsubstrates. For example, the coating composition may be used to formcoatings on metal substrates for containers of food and beverageproducts (or other packaged products), and methods for producing thecoating composition. The present disclosure is also directed tocontainers having coatings formed from the coating composition, andrelated methods of application.

The coating composition of the present disclosure includes a latexemulsion, and may optionally be further formulated to include one ormore additional additives. The coating composition may also optionallybe rheologically modified for different coating applications (e.g.,diluted or otherwise configured for spray coating applications).

The latex emulsion of the coating composition preferably includescopolymers that are polymerized in multiple separate emulsionpolymerization stages. In some embodiments, one or more polymerizablesurfactant monomers are used. As discussed below, the resulting coatingcomposition is believed to produce cured coatings having a desirablebalance of coating properties, including good corrosion resistance,flexibility, and durability, rendering the coating compositionparticularly suitable for forming coatings that can be used in a varietyof different products (e.g., packaging containers for food and beverageproducts). In fact, the coating composition is particularly suitable foruse in a spray coating applications to coat interior surfaces ofcontainers for food and beverage products, including food and beverageproducts that are chemically aggressive.

The latex emulsion is preferably produced in a multiple-stage process,which may be based on an inverted core-shell polymerization process inwhich it is believed that portions of the latex particle which tend toassociate towards the outside of the particle are formed prior toportions that tend to associate towards the interior of the particle,and which is discussed in more detail below. Briefly, in preferredembodiments, the first-stage polymerization preferably involves emulsionpolymerizing first-stage monomers (optionally including one or morepolymerizable and/or non-polymerizable surfactant monomers) in anaqueous carrier to produce first-stage copolymers. This is believed toproduce copolymers having higher molecular weights (as compared, e.g.,to solution polymerized copolymers). Alternatively, polymers that wereformed in organic solution prior to dispersal in the aqueous carrier maybe employed (e.g., solution polymerized acrylic, polyester, alkyd,and/or polyurethane polymers or copolymers thereof).

From there, a second-stage emulsion polymerization may be conducted,where second-stage monomers may be emulsion polymerized in the presenceof the first-stage copolymers. Additionally, the second stage copolymersmay include curing groups, which are preferably functional groups thatcompliment and graft to step-growth functional groups of the first-stagecopolymers during a subsequent curing step, preferably via a step-growthreaction. This forms cured linkages, which can crosslink the first-stagecopolymers and the second-stage copolymers, during coating cure.

The latex emulsion produced from the above-discussed process may then beoptionally further formulated and/or modified for different coatingapplications, thereby producing the coating composition of the presentdisclosure. The coating composition may then be applied to a metalsubstrate (or other suitable substrate), either before or after thesubstrate is formed into a food or beverage container (e.g., two-piececans, three-piece cans) or a portion thereof (e.g., a food can orbeverage can end), whether it be a can end or can body. The appliedcoating composition may then be cured on the metal substrate to producea coating.

The following is an example of a two-stage polymerization process (whichmay optionally include one or more additional stages) for producing thelatex emulsion, for formulating a coating composition therefrom, and forforming cured coatings therefrom. In some embodiments, thepolymerization process may function in a core-shell polymerizationreaction, such as an inverse core-shell reaction where the first-stagecopolymers form a shell portion and the second-stage copolymers form acore portion.

Additionally, prior to the first-stage polymerization, the multi-stagepolymerization process may include one or more seed polymerizationstages to form polymerized seeds from seed monomers. Examples ofsuitable seed monomers include those discussed below for the first-stagemonomers. More preferably, less than about 10% by weight of the overalllatex copolymer is formed by seed polymerization stage(s), even morepreferably less than about 5% by weight, and even more preferably lessthan about 1% by weight. In some embodiments, substantially none of theoverall latex copolymer is formed by seed polymerization stage(s).

During the first-stage polymerization, first-stage monomers may bedispersed or otherwise suspended in an aqueous carrier. In preferredembodiments, the first-stage polymerization may be an emulsionpolymerization process that produces first-stage copolymers from thefirst-stage monomers dispersed in the aqueous carrier, optionally withthe use of one or more surfactants. Preferred first-stage copolymers arecapable of facilitating emulsification and/or polymerization of thesecond stage monomers.

The first-stage monomers preferably include a mixture of monomerscapable of polymerizing under free radical-initiated emulsionpolymerization conditions, such as monomers havingethylenically-unsaturated groups. Specific examples of suitable monomershaving ethylenically-unsaturated groups include (meth)acrylate monomers,ethylenically-unsaturated monomers having at least one functional groupcapable of participating in a step-growth reaction (referred to hereinas “step-growth functional monomers”), ethylenically-unsaturatedaromatic monomers, ethylenically-unsaturated polymerizable surfactants,and mixtures thereof.

In certain preferred embodiments, the first-stage copolymer includeswater-dispersing groups (e.g., salt or salt-forming groups) and morepreferably a sufficient amount of water-dispersing groups so that thefirst-stage copolymer can function as a polymeric surfactant tofacilitate the emulsion polymerization of the second-stage monomers.

Suitable (meth)acrylates for the first-stage monomers include thosehaving the following structure:

where group R₁ may be a hydrogen atom or an organic group, such as aC₁-C₆ alkyl group, and more preferably a hydrogen atom or a methylgroup. Additionally, one or both of the hydrogen atoms attached to theterminal carbon atom of the ethylenically-unsaturated group may bereplaced with an independant group R₁. Groups R₂ and R₃ may eachindependantly be any suitable organic group, such as, for example, aC₁-C₁₆ alkyl or alkenyl group, which can be substituted with one or more(e.g., 1-3) groups such as hydroxy group, halogen groups, phenyl groups,oxirane groups, and alkoxy groups, for example. The integer “n” may bezero or one, more preferably zero such that group R₂ is omitted and theester (—COOR₃) group extends directly from the unsaturated group.

Specific examples of suitable (meth)acrylates encompass alkyl(meth)acrylates, which are preferably esters of acrylic or methacrylicacid. Examples of suitable alkyl (meth)acrylates include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl(meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, decyl(meth)acrylate, isodecyl (meth)acrylate, benzyl (meth)acrylate, lauryl(meth)acrylate, isobornyl (meth)acrylate, octyl (meth)acrylate, nonyl(meth)acrylate, hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate(HEMA), hydroxypropyl (meth)acrylate (HPMA), and mixtures thereof.Difunctional (meth)acrylate monomers may be used in the monomer mixtureas well. Examples include ethylene glycol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, allyl methacrylate, and the like.

The one or more (meth)acrylates may constitute greater than about 5%,more preferably greater than about 10%, and even more preferably greaterthan about 20% by weight of the first-stage monomers used to produce thefirst-stage copolymers. The (meth)acrylates may also constitute lessthan about 70%, more preferably less than about 50%, and even morepreferably less than about 30% by weight of the first-stage monomersused to produce the first-stage copolymers.

Examples of suitable ethylenically-unsaturated step-growth-functionalmonomers include ethylenically-unsaturated acid-functional monomershaving at least one functional group capable of participating in astep-growth reaction, ethylenically-unsaturated alcohol-functionalmonomers, ethylenically-unsaturated amine-functional monomers, andethylenically-unsaturated amide-functional monomers, and mixturesthereof. Preferably, the ethylenically-unsaturatedstep-growth-functional monomers are ethylenically-unsaturatedacid-functional monomers, which may be included to provide acidfunctional groups to the resulting first-stage copolymers. As discussedbelow, the acid functional groups may assist in water dispersibility(e.g., via neutralization) and may also provide step-growth reactionsites during the curing steps.

Examples of suitable ethylenically-unsaturated acid-functional monomersinclude ethylenically-unsaturated carboxylic acid monomers, anhydridesthereof, salts thereof, and mixtures thereof Illustrativeethylenically-unsaturated carboxylic acid monomers include thoserepresented by the following structure:

where the group R₄ may be a hydrogen atom or an organic group, such as aC₁-C₆ alkyl group, and more preferably a hydrogen atom or a methylgroup. Additionally, one or both of the hydrogen atoms attached to theterminal carbon atom of the ethylenically-unsaturated group may bereplaced with an independant group R₄. Group R₅ may be any suitabledivalent group, such as, for example, a C₁-C₁₆ alkyl or alkenyl group,which can be substituted with one or more (e.g., 1-3) groups such ashydroxy group, halogen groups, phenyl groups, oxirane groups, and alkoxygroups, for example. The integer “n” may be zero or one, more preferablyzero such that group R₅ is omitted and the carboxyl (—COOH) groupextends directly from the unsaturated group.

Examples of suitable ethylenically-unsaturated carboxylic acid monomersinclude acrylic acid, methacrylic acid, alpha-chloroacrylic acid,alpha-cyanoacrylic acid, crotonic acid, alpha-phenylacrylic acid,beta-acryloxypropionic acid, fumaric acid, maleic acid, sorbic acid,alpha-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamicacid, beta-stearylacrylic acid, citraconic acid, mesaconic acid,glutaconic acid, aconitic acid, tricarboxyethylene, 2-methyl maleicacid, itaconic acid, 2-methyl itaconic acid, methyleneglutaric acid, andthe like, and mixtures thereof. Preferred ethylenically-unsaturatedcarboxylic acid monomers include acrylic acid, methacrylic acid,crotonic acid, fumaric acid, maleic acid, 2-methyl maleic acid, itaconicacid, 2-methyl itaconic acid, and mixtures thereof.

Examples of suitable ethylenically-unsaturated anhydride monomersinclude compounds derived from the above-discussedethylenically-unsaturated carboxylic acid monomers (e.g., as pureanhydride or mixtures of such). Preferred ethylenically-unsaturatedanhydrides include acrylic anhydride, methacrylic anhydride, and maleicanhydride. If desired, aqueous salts of the aboveethylenically-unsaturated carboxylic acid monomers may also be employed.

Examples of suitable ethylenically-unsaturated alcohol-functionalmonomers include monomers having ethylenically-unsaturated groups andone or more alcohol (—COH) groups. Illustrative alcohol-functionalmonomers include those represented by the following structure:

where the group R₆ may be a hydrogen atom or an organic group, such as aC₁-C₆ alkyl group, and more preferably a hydrogen atom or a methylgroup. Additionally, one or both of the hydrogen atoms attached to theterminal carbon atom of the ethylenically-unsaturated group may bereplaced with an independant group R₆. Group R₇ may be any suitabledivalent group, such as, for example, a C₁-C₁₆ alkyl or alkenyl group,which can be substituted with one or more (e.g., 1-3) groups such ashydroxy group, halogen groups, phenyl groups, oxirane groups, and alkoxygroups, for example. The integer “n” may be zero or one, more preferablyzero such that group R₇ is omitted and the alcohol (—COH) group extendsdirectly from the unsaturated group.

In some embodiments, the first-stage monomers may also includeethylenically-unsaturated amine-functional monomers and/orethylenically-unsaturated amide-functional monomers, such as thosehaving one or more vinyl groups and one or more amine and/or amidegroups. Preferably, the amide functional groups undergo hydrolysis afterthe first-stage polymerization to produce amine-functional groups forthe first-stage copolymers.

These monomers may provide amine-functional groups that can react withsome embodied curing monomers (e.g., cyclocarbonates) using astep-growth reaction, during the subsequent curing step. Theconcentration ranges of the ethylenically-unsaturated amine-functionalmonomers and ethylenically-unsaturated amide-functional monomers arepreferably included in the above-discussed collective concentrations ofthe ethylenically-unsaturated acid-functional monomers and theethylenically-unsaturated alcohol-functional monomers. However, in someembodiments, the coating composition of the present disclosure issubstantially free or completely free of amide-functional materials(e.g., acrylamides).

The ethylenically-unsaturated step-growth-functional monomers maycollectively constitute greater than about 5%, more preferably greaterthan about 10%, and even more preferably greater than about 20% byweight of the first-stage monomers used to produce the first-stagecopolymers. The ethylenically-unsaturated step-growth-functionalmonomers may also collectively constitute less than about 50%, morepreferably less than about 40%, even more preferably less than about35%, and even more preferably less than about 30% by weight of thefirst-stage monomers used to produce the first-stage copolymers.

As mentioned above, at least some (and optionally all) of theethylenically-unsaturated step-growth-functional monomers are preferablyethylenically-unsaturated acid-functional monomers. As such, preferredweight ranges for the ethylenically-unsaturated acid-functional monomersrelative to the first-stage monomers used to produce the first-stagecopolymers include those discussed above for theethylenically-unsaturated step-growth-functional monomers. In someembodiments, the ethylenically-unsaturated step-growth-functionalmonomers include both acid-functional monomers and monomers having otherfunctional groups (e.g., —OH, —NCO, —NH₂, oxirane, etc. . . . . ).

Suitable ethylenically-unsaturated aromatic monomers include monomershaving aromatic groups and ethylenically-unsaturated groups (e.g.,aromatic vinyl monomers). Examples of suitable ethylenically-unsaturatedaromatic monomers include styrene, methyl styrene, halostyrene,diallylphthalate, divinylbenzene, alpha-methylstyrene, vinyl toluene,vinyl naphthalene, and mixtures thereof. Styrene is a presentlypreferred vinyl monomer, in part due to its relatively low cost.However, in some embodiments, the first-stage monomers may besubstantially free or completely free of styrene.

The ethylenically-unsaturated aromatic monomers may constitute greaterthan about 20%, more preferably greater than about 30%, even morepreferably greater than about 40%, and even more preferably greater thanabout 45% by weight of the first-stage monomers used to produce thefirst-stage copolymers. The ethylenically-unsaturated aromatic monomersmay also constitute less than about 70%, more preferably less than about60%, and even more preferably less than about 55% by weight of thefirst-stage monomers used to produce the first-stage copolymers.

As can be appreciated, some of the above-described monomers may fallwithin multiple monomer categories. For example, some of the monomersmay qualify as both a meth(acrylate) monomer and anethylenically-unsaturated aromatic monomer, such as benzyl(meth)acrylate. Similarly, others of the monomers may qualify as both anethylenically-unsaturated acid-functional monomer and anethylenically-unsaturated aromatic monomer, such as cinnamic acid. Inthese situations, unless expressly stated otherwise, the above-discussedconcentration ranges for the ethylenically-unsaturated aromatic monomersencompasses all aromatic monomers of the first-stage monomers, includingthose that also qualify as meth(acrylate) monomers,ethylenically-unsaturated acid-functional monomers, and/orethylenically-unsaturated alcohol-functional monomers.

The one or more surfactant monomers (which may be polymerizable ornon-polymerizable) may assist in dispersing the first-stage monomers inthe aqueous carrier, as well as optionally polymerizing with each otherand/or the above-discussed first-stage monomers to form chain segmentsof the first-stage copolymers and/or with subsequent stage monomers. Thesurfactant monomers preferably include hydrophobic and hydrophilicportions. The polymerizable surfactant monomers are preferably capableof polymerizing under free radical-initiated polymerization conditions,such as surfactant monomers having ethylenically-unsaturated groups(e.g., (meth)acrylic-based polymerizable surfactant monomers). Examplesof polymerizable surfactant monomers for use in the latex emulsion mayinclude those having one or more hydrophobic portions, one or morehydrophilic portions, and one or more ethylenically-unsaturated groupmay be located at the hydrophobic portion, at the hydrophilic portion,or in-between.

The hydrophobic portion(s) may be any suitable substituted orunsubstituted hydrocarbon chain, such as a substituted or unsubstitutedalkyl or alkenyl group, a substituted or unsubstituted cyclichydrocarbon group, a substituted or unsubstituted aromatic hydrocarbongroup, and combinations thereof. The hydrophobic portion preferablyinclude one or more non-polar groups, such as one or more aromaticgroups.

The hydrophilic portion(s) may be any suitable substituted orunsubstituted hydrocarbon chain, such as a substituted or unsubstitutedalkyl or alkenyl chain, optionally with one or more ether linkages,which terminates in a polar group. The polar group may include one ormore hydroxyl groups, acid groups (e.g., carboxylic acid groups),sulfonate groups, sulfinate groups, sulfate groups, phosphate groups,phosphinate groups, phosphonate groups, salt derivatives thereof, andcombinations thereof.

Examples of suitable polymerizable surfactant monomers include thosedisclosed in U.S. Publication No. 2002/0155235; and those commerciallyavailable under the tradename “REASOAP” from Adeka Corporation, Tokyo,Japan., under the tradenames “NOIGEN” and “HITENOL” from Da-Ichi KogyoSiyyaku Co., Ltd., Tokyo, Japan; and under the tradename “SIPOMER” fromSolvay Rhodia, Brussels, Belgium. In embodiments that includepolymerizable surfactant monomers, the polymerizable surfactant monomersmay constitute greater than about 0.1%, more preferably greater thanabout 0.5%, and even more preferably greater than about 1% by weight ofthe first-stage monomers used to produce the first-stage copolymers. Thepolymerizable surfactant monomers may also constitute less than about15%, more preferably less than about 10%, and even more preferably lessthan about 5% by weight of the first-stage monomers used to produce thefirst-stage copolymers.

More preferably, the first-stage monomers include a combination of oneor more: (meth)acrylate monomers, one or more ethylenically-unsaturatedacid-functional monomers, one or more ethylenically-unsaturated aromaticmonomers, and one or more polymerizable surfactant monomers.

A first particularly suitable combination of first-stage monomersincludes one or more non-aromatic (meth)acrylates, one or more(meth)acrylic acids, one or more vinyl aromatic monomers, and optionallyone or more ethylenically-unsaturated polymerizable surfactant monomers.In this first particularly suitable combination, the non-aromatic(meth)acrylates may constitute from about 5% to about 40% by weight, andmore preferably from about 15% to about 30% by weight; the (meth)acrylicacids may constitute from about 15% to about 40% by weight, and morepreferably from about 20% to about 30% by weight; the vinyl aromaticmonomers may constitute from about 35% to about 65% by weight, and morepreferably from about 45% to about 55% by weight; and the optionalethylenically-unsaturated polymerizable surfactant monomer mayconstitute from 0% to about 10% by weight, and more preferably fromabout 1% to about 5% by weight; based on the entire weight of thefirst-stage monomers used to produce the first-stage copolymers.

A second particularly suitable combination of first-stage monomersincludes one or more non-aromatic (meth)acrylates, one or more(meth)acrylic acids, one or more aromatic (meth)acrylates, andoptionally one or more ethylenically-unsaturated polymerizablesurfactant monomers, and is substantially free of styrene. Thisembodiment illustrates an example coating composition that issubstantially free of styrene, where the aromatic functionality isobtained with one or more aromatic (meth)acrylates (e.g., benzylmethacrylate).

In this second particularly suitable combination, the non-aromatic(meth)acrylates may constitute from about 5% to about 30% by weight, andmore preferably from about 15% to about 25% by weight; the (meth)acrylicacids may constitute from about 10% to about 40% by weight, and morepreferably from about 15% to about 30% by weight; the aromatic(meth)acrylates may constitute from about 40% to about 70% by weight,and more preferably from about 50% to about 65% by weight; and theoptional ethylenically-unsaturated polymerizable surfactant monomers mayconstitute from 0% to about 10% by weight, and more preferably fromabout 1% to about 5% by weight; based on the entire weight of thefirst-stage monomers used to produce the first-stage copolymers.

The aqueous carrier may include water, and optionally, one or moreorganic solvents. Examples of suitable organic solvents for use in theaqueous carrier may include methanol, ethanol, isopropyl alcohol, butylalcohols (e.g., n-butanol and buytl glycol), 2-butoxyethanol,2-(2-butoxyethoxy)ethanol (i.e., butyl carbitol), aromatic solvents,isophorones, glycol ethers, glycol ether acetates, acetone, methyl-ethylketones (MEK), N,N-dimethylformamides, ethylene carbonates, propylenecarbonates, diglymes, N-methylpyrrolidones (NMP), ethyl acetates,ethylene diacetates, propylene glycol diacetates, alkyl ethers ofethylene, propylene glycol monoacetates, toluene, xylenes, andcombinations thereof

Optionally, one or more non-polymerizable surfactants may also be used(i.e., alone or in combination with one or more polymerizablesurfactants), such as surfactants that can support emulsionpolymerization reactions. For example, the non-polymerizablesurfactant(s) may include surfactants containing sulfonate groups,sulfate groups, phosphate groups, phosphinate groups, phosphonategroups, and combinations thereof; as well as ethoxylated surfactants. Anexample of a non-polymerizable surfactant includes dodecylbenzenesulfonic acid and sulfonates thereof (e.g., dodecylbenzene sulfonatesalts, and particularly amine-neutralized salts).

The concentration of non-polymerizable surfactants may vary depending onthe types and concentrations of the monomers used during the first-stagepolymerization, including the polymerizable surfactant monomers. Inembodiments that include non-polymerizable surfactants, thenon-polymerizable surfactants may constitute greater than about 0.01%,more preferably greater than about 0.05%, and even more preferablygreater than about 0.1% by weight, relative to a total weight of thefirst-stage monomers. The non-polymerizable surfactants may alsoconstitute less than about 10%, more preferably less than about 7%, andeven more preferably less than about 5% by weight, relative to the totalweight of the first-stage monomers.

The surfactants used herein are preferably non-long-chain-polymersurfactants, such as polymerizable surfactant monomers and/ornon-polymerizable surfactants having molecular weights less than about2,000, and more preferably less than about 1,000.

In alternative embodiments, the first-stage polymerization may beperformed as an emulsion polymerization process without the use of anypolymerizable or non-polymerizable surfactants. Some extra stabilizationof the latex is thought to be due to the incorporation in the polymer ofionic species coming from the initiators. For example, somepersulphate-based initiators, such as ammonium persulphate, may functionas stabilizers of the latex.

In these embodiments, the dispersant compounds are preferably used inconcentrations greater than about 0.01%, more preferably greater thanabout 0.1%, and even more preferably greater than about 0.3% by weight,relative to the total weight of the first-stage monomers. The initiatorand accelerator are also preferably used in concentrations less thanabout 10%, more preferably less than about 5%, and even more preferablyless than about 3% by weight, relative to the total weight of thefirst-stage monomers.

For an emulsion polymerization process conducted during the first-stagepolymerization, the one or more surfactants (or alternative dispersantcompounds) may be initially dispersed in the aqueous carrier, which ispreferably accompanied by agitation of the aqueous carrier.Additionally, the resulting surfactant dispersion is preferably heatedto assist in the subsequent polymerization reactions. Preferredtemperatures for heating the surfactant dispersion include temperaturesgreater than about 65° C., and more preferably from about 70° C. toabout 90° C. The pH of the dispersion may be maintained at any suitablelevel, such as from about 5 to about 12. The first-stage monomers andthe one or more surfactants may be added to the reaction mixture at anysuitable time relative to one another—e.g., simultaneous addition, theaddition of surfactant prior to the addition of monomer, and/or theaddition of surfactant after the addition of monomer.

When the aqueous dispersion reaches the desired temperature, theremaining first-stage monomers may be introduced to the dispersion. Thefirst-stage monomers may be added incrementally or continuously to theaqueous dispersion over time. Alternatively, in certain embodiments abatch or semi-batch process may be used to polymerize the first-stagemonomers in the aqueous dispersion, as described in O'Brien et al., U.S.Pat. No. 8,092,876.

One or more polymerization initiators may also be added to the aqueousdispersion (e.g., along with the first-stage monomers) to initiate thefirst-stage polymerization. Suitable polymerization initiators includefree-radical initiators, such as one or more peroxides and/orpersulfates and similar compounds. Examples of suitable peroxidesinclude hydroperoxides such as t-butyl hydroperoxide, hydrogen peroxide,t-amyl hydroperoxide, methyl hydroperoxide, and cumene hydroperoxide;peroxides such as benzoyl peroxide, caprylyl peroxide, di-t-butylperoxide, ethyl 3,3′-di(t-butylperoxy) butyrate, ethyl3,3′-di(t-amylperoxy) butyrate, t-amylperoxy-2-ethyl hexanoate, andt-butylperoxy pivilate; peresters such as t-butyl peracetate, t-butylperphthalate, and t-butyl perbenzoate; as well as percarbonates; andmixtures thereof. Azoic compounds can also be used to generate freeradicals such as 2,2′-azo-bis(isobutyronitrile),2,2′-azo-bis(2,4-dimethylvaleronitrile), and1-t-butyl-azocyanocyclohexane, and mixtures thereof. Examples ofsuitable persulfates include persulfates of ammonium or alkali metal(potassium, sodium or lithium). Perphosphates can be also a source offree radicals, and mixtures thereof.

Polymerization initiators can be used alone or as the oxidizingcomponent of a redox system, which also typically includes a reducingcomponent such as ascorbic acid, malic acid, glycolic acid, oxalic acid,lactic acid, thiogycolic acid, or an alkali metal sulfite, morespecifically a hydrosulfite, hyposulfite or metabisulfite, such assodium hydrosulfite, potassium hyposulfite and potassium metabisulfite,or sodium formaldehyde sulfoxylate, ferrous complexes (e.g., ferroussulphate heptahydrate), and mixtures thereof. The reducing component isfrequently referred to as an accelerator or a catalyst activator.

The initiator and accelerator (if used) are preferably each used inconcentrations greater than about 0.001%, more preferably greater thanabout 0.1%, and even more preferably greater than about 1% by weight,relative to the total weight of the first-stage monomers. The initiatorand accelerator (if used) are also each preferably used inconcentrations less than about 10%, more preferably less than about 7%,and even more preferably less than about 5% by weight, relative to thetotal weight of the first-stage monomers.

Promoters such as chloride and sulfate salts of cobalt, iron, nickel orcopper can be used in small amounts, if desired. Examples of redoxcatalyst systems include tert-butyl hydroperoxide/sodium formaldehydesulfoxylate/Fe(II), and ammonium persulfate/sodium bisulfate/sodiumhydrosulfite/Fe(II).

The first stage polymerization may continue for a suitable duration topolymerize the first-stage monomers with a free-radical initiatedpolymerization process. This produces the first-stage copolymers, whichmay be linear, branched, or combinations thereof

In preferred embodiments, due to the inclusion of theethylenically-unsaturated step-growth-functional monomers, at leastsome, and more preferably substantially each of the first-stagecopolymers have one or more step-growth-functional groups, such as oneor more acid-functional groups (e.g., pendant carboxylic acid groupsand/or anhydride groups), one or more alcohol-functional groups, and/orone or more amine-functional groups. As discussed below, in someembodiments, at least a portion of these step-growth-functional groupsmay subsequently react with the curing groups of the second-stagecopolymers during a curing step and/or function as water dispersinggroups (e.g., when neutralized).

In embodiments in which the first-stage copolymer includesacid-functional step-growth-functional monomers, after the first-stagepolymerization is completed, at least a portion of the carboxylic acidgroups and/or anhydride groups of the first-stage copolymers may beneutralized or partially neutralized with a suitable basic compound toproduce water-dispersing groups. Alternatively (or additionally), insome embodiments, one or more the first-stage monomers may bepre-neutralized prior to the first-stage polymerization.

The basic compound used for neutralization is preferably a fugitivebase, more preferably an amine fugitive base (e.g., primary, secondary,and/or tertiary amines), with tertiary amines being particularlypreferred. Some examples of suitable tertiary amines are trimethylamine, dimethylethanol amine (also known as dimethylamino ethanol),methyldiethanol amine, triethanol amine, ethyl methyl ethanol amine,dimethyl ethyl amine, dimethyl propyl amine, dimethyl 3-hydroxy-1-propylamine, dimethylbenzyl amine, dimethyl 2-hydroxy-1-propyl amine, diethylmethyl amine, dimethyl 1-hydroxy-2-propyl amine, triethyl amine,tributyl amine, N-methyl morpholine, and mixtures thereof. Triethylamine and dimethyl ethanol amine are preferred tertiary amines.

The degree of neutralization required may vary considerably dependingupon the amount of acid or base groups included in the first-stagecopolymers, and the degree of dispersibility that is desired. Inembodiments in which neutralized acid groups are used for waterdispersibility, preferred acid numbers for the first-stage copolymerprior to neutralization include acid numbers greater than about 40, morepreferably greater than about 80, and even more preferably greater thanabout 100 milligrams (mg) potassium hydroxide (KOH) per gram of thefirst-stage copolymer. Preferred acid numbers for the first-stagecopolymer prior to neutralization also include acid numbers less thanabout 400, more preferably less than about 350, and even more preferablyless than about 300 mg KOH per gram of the first-stage copolymer. Acidnumbers referred to herein may be calculated pursuant to BS EN ISO3682-1998 standard, or alternatively may be theoretically determinedbased on the reactant monomers.

Typically, to render the first-stage copolymers water-dispersible, atleast 25% of the acid groups of the first-stage copolymers areneutralized, preferably at least 30% are neutralized, and morepreferably at least 35% are neutralized. Preferably, the first-stagecopolymers include a sufficient number of water-dispersing groups toform a stable dispersion in the aqueous carrier. Furthermore, inembodiments incorporating polymerizable surfactant monomer and/or othersurfactant, the hydrophilic portions of the surfactant may also assistin dispersing the first-stage copolymers in the aqueous carrier.

While the first-stage copolymers have been primarily described hereinwith acid-based water-dispersing groups that are neutralized with basiccompounds, in alternative embodiments, the water-dispersing groups maybe basic groups that are neutralized with acidic compounds. Examples ofsuitable basic groups for this embodiment include those disclosed inO'Brien et al., U.S. Pat. No. 8,092,876. Examples of suitable acidicneutralizing compounds include formic acid, acetic acid, hydrochloricacid, sulfuric acid, and mixtures thereof.

Preferred number-average molecular weights for the first-stage copolymerin this emulsion-polymerized embodiment include those greater than about50,000, more preferably greater than about 100,000, even more preferablygreater than about 500,000, and even more preferably greater than about1,000,000.

Preferred glass transition temperatures for the first-stage copolymer inthis emulsion-polymerized embodiment include those greater than about40° C., more preferably greater than about 45° C., even more preferablygreater than about 50° C., and most preferably greater than about 60° C.Preferred glass transition temperatures for the first-stage copolymer inthis emulsion-polymerized embodiment include those less than about 120°C., more preferably less than about 100° C., even more preferably lessthan about 90° C., and even more preferably less than about 80° C. Theglass transition temperatures referred to herein are theoreticallycalculated pursuant to the Flory-Fox Equation.

After the first-stage polymerization is completed, the second stagepolymerization may be conducted to produce the second-stage copolymers.As discussed above, this may be performed with an inverse core-shellarrangement, where the first-stage copolymers generally define an outerportion of the latex emulsion and the second-stage copolymers generallydefine a core of the late emulsion inside of the shell.

In some embodiments, the first and second stage polymerizations may atleast partially overlap. For example, the second-stage polymerizationmay start after at least about 50% by weight of the first-stage monomersare polymerized, more preferably after at least about 75% by weight, andeven more preferably after at least about 90% by weight. In someembodiments, the second-stage polymerization may start after thefirst-stage polymerization is completed.

The second-stage polymerization may initially involve addingsecond-stage monomers and a suitable polymerization initiator to theaqueous dispersion containing the first-stage copolymers (which arepreferably at least partially neutralized), where examples of suitablepolymerization initiators and their concentrations for the second-stagepolymerization include those discussed above for the first-stagepolymerization.

The second-stage monomers may include the same types ofethylenically-unsaturated monomers as used for the first-stage monomers,such as one or more (meth)acrylate monomers, optionally one or more ofethylenically-unsaturated step-growth-functional monomers, andoptionally one or more ethylenically-unsaturated aromatic monomers. Suchethylenically-unsaturated monomers for the second-stage monomers includethose discussed above for the first-stage monomers. In preferredembodiments, the second-stage monomers are, when considered overall,more hydrophobic relative to those of the first-stage copolymer.

Furthermore, in some preferred embodiments, the second-stage monomersare chemically different from the first-stage monomers, such that thesecond-stage copolymer is chemically different from the first-stagecopolymer. For example, at least about 5%, more preferably at leastabout 10% by weight of the first-stage monomers are different than thesecond-stage monomers.

The (meth)acrylate monomers may constitute greater than about 5%, morepreferably greater than about 10%, and even more preferably greater thanabout 15% by weight of the second-stage monomers used to produce thesecond-stage copolymers. (Meth)acrylate monomers may also constituteless than about 55%, more preferably less than about 40%, and even morepreferably less than about 35% by weight of the second-stage monomersused to produce the second-stage copolymers.

In some preferred embodiments, the second-stage monomers aresubstantially free of ethylenically-unsaturated step-growth-functionalmonomers (e.g., substantially free of ethylenically-unsaturatedacid-functional monomers). Instead, the second-stage monomers preferablyinclude one or more curing monomers, which may undergo step-growthreactions during a subsequent curing step to form a cured coating.

The curing monomer preferably includes at least two different functionalgroups. The first functional group of the curing monomer preferablycompliments the step-growth-functional groups of the first-stagecopolymers (e.g., the acid-, alcohol-, and amine-functional groups),thereby allowing the first functional group to react with one of thestep-growth-functional groups via a step-growth reaction (i.e., during asubsequent curing step). Examples of preferred groups for the firstfunctional group of the linkage monomer include oxirane groups,isocyanate groups, azlactone groups, oxazoline groups, cyclocarbonategroups, and the like.

In comparison, the second functional group of the curing monomer ispreferably configured to react with the second-stage monomers.Accordingly, examples of preferred groups for the second functionalgroup include ethylenically-unsaturated groups, such as vinyl groups.

In some preferred embodiments, the first functional group is an oxiranegroup, such as in an oxirane-containing ethylenically-unsaturatedmonomers. Examples of suitable curing monomers containing oxirane groupsinclude glycidyl esters of alpha, beta-unsaturated acids, or anhydridethereof (e.g., an oxirane group-containing alpha, beta-ethylenicallyunsaturated monomer). Suitable alpha, beta-unsaturated acids includemonocarboxylic acids or dicarboxylic acids. Examples of such carboxylicacids include acrylic acid, methacrylic acid, alpha-chloroacrylic acid,alpha-cyanoacrylic acid, beta-methylacrylic acid (crotonic acid),alpha-phenylacrylic acid, beta-acryloxypropionic acid, sorbic acid,alpha-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamicacid, beta-stearylacrylic acid, itaconic acid, citraconic acid,mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaricacid, tricarboxyethylene, maleic anhydride, and mixtures thereof

Specific examples of suitable curing monomers containing a glycidylgroup are glycidyl (meth)acrylate (e.g., glycidyl methacrylate andglycidyl acrylate), mono- and di-glycidyl itaconate, mono- anddi-glycidyl maleate, and mono- and di-glycidyl formate. A preferredlinkage monomer is glycidyl methacrylate (“GMA”).

In other embodiments, the first functional group may be an isocyanategroup. In these embodiments, examples of suitable curing monomersinclude ethylenically-unsaturated isocyanate monomers, such as vinylisocyanates (e.g., isopropenyl dimethylbenzyl isocyanate from CytecIndustries, Inc., Woodland Park, NJ). The isocyanate groups preferablycompliment first-stage copolymers having acid-functional groups and/oralcohol-functional groups, more preferably alcohol-functional groups,which can undergo step-growth reactions with the isocyanate groups.

In further embodiments, the first functional group may be an azlactoneor an oxazoline group. In these embodiments, examples of suitable curingmonomers include ethylenically-unsaturated azlactone monomers (e.g.,vinyl azlactones, such as those available from Isochem SAS, 3 RueLavoisier, 91710-Vert le Petit, France) and ethylenically-unsaturatedoxazoline monomers (e.g., vinyl oxazolines, such as those available fromSigma Aldrich). The azlactone and oxazoline groups preferably complimentfirst-stage copolymers having acid-functional groups, which can undergostep-growth reactions with the azlactone groups or the oxazoline groups.

In other embodiments, the first functional group may be ancyclocarbonate group. In these embodiments, examples of suitable curingmonomers include ethylenically-unsaturated cyclocarbonate monomers, suchas vinyl cyclocarbonates (e.g., vynilidene carbonate, andcyclocarbolates obtained by carbonization of glycidyl methacrylate). Thecyclocarbonate groups preferably compliment first-stage copolymershaving amine-functional groups, which can undergo step-growth reactionswith the cyclocarbonate groups.

The curing monomers, if present, may constitute, for example, greaterthan about 5%, more preferably greater than about 10%, and even morepreferably greater than about 15% by weight of the second-stage monomersused to produce the second-stage copolymers. The curing monomers mayalso constitute less than about 40%, more preferably less than about30%, and even more preferably less than about 25% by weight of thesecond-stage monomers used to produce the second-stage copolymers.

The ethylenically-unsaturated aromatic monomers, if present, mayconstitute, for example, greater than about 20%, more preferably greaterthan about 35%, and even more preferably greater than about 50% byweight of the second-stage monomers used to produce the second-stagecopolymers. The ethylenically-unsaturated aromatic monomers may alsoconstitute less than about 80%, more preferably less than about 75%, andeven more preferably less than about 65% by weight of the second-stagemonomers used to produce the second-stage copolymers.

Some of the above-described second-stage monomers may also fall withinmultiple monomer categories. For example, some of the monomers mayqualify as both a meth(acrylate) monomer and anethylenically-unsaturated aromatic monomer, such as benzyl(meth)acrylate. In these situations, unless expressly stated otherwise,the above-discussed concentration ranges for theethylenically-unsaturated aromatic monomers encompasses all aromaticmonomers of the second-stage monomers, including those that also qualifyas meth(acrylate) monomers, ethylenically-unsaturated acid-functionalmonomers, ethylenically-unsaturated alcohol-functional monomers,ethylenically-unsaturated amine/amide-functional monomers and/or thecuring monomers.

More preferably, the second-stage monomers include a combination of oneor more non-aromatic (meth)acrylate monomers, one or moreethylenically-unsaturated aromatic monomers, and one or more curingmonomers.

A first particularly suitable combination of second-stage monomersincludes one or more non-aromatic (meth)acrylates, one or more vinylaromatic monomers, and one or more oxirane-containing (meth)acrylates.In this first particularly suitable combination, the non-aromatic(meth)acrylates may constitute from about 5% to about 40% by weight, andmore preferably from about 10% to about 30% by weight; the vinylaromatic monomers may constitute from about 35% to about 75% by weight,and more preferably from about 50% to about 65% by weight; and theoxirane-containing (meth)acrylates may constitute from about 5% to about30% by weight, and more preferably from about 10% to about 25% byweight; based on the entire weight of the second-stage monomers used toproduce the second-stage copolymers.

A second particularly suitable combination of second-stage monomersincludes one or more non-aromatic (methyl)acrylates, one or morearomatic (meth)acrylates, and one or more oxirane-containing(meth)acrylates, wherein the second-stage monomers are substantiallyfree of styrene. This embodiment illustrates an example coatingcomposition that is substantially free of styrene, where aromaticfunctionality is obtained with an aromatic (meth)acrylate (e.g., benzylmethacrylate). In this second particularly suitable combination, thenon-aromatic (methyl)acrylates may constitute from about 10% to about55% by weight, and more preferably from about 20% to about 40% byweight; the aromatic (meth)acrylates may constitute from about 30% toabout 60% by weight, and more preferably from about 40% to about 50% byweight; and the oxirane-containing (meth)acrylates may constitute fromabout 5% to about 30% by weight, and more preferably from about 10% toabout 25% by weight; based on the entire weight of the second-stagemonomers used to produce the second-stage copolymers.

In some embodiments, the first and second particularly suitablecombinations include, if any, less than 5%, more preferably less than2%, even more preferably less than 1% of acid-functional monomer.

The second-stage polymerization may continue for a suitable duration topolymerize the second-stage monomers with a free-radical initiatedpolymerization process. The resulting second-stage copolymers, may belinear, branched, or combinations thereof. For example, the curingmonomers preferably polymerize with other second-stage monomers to formpendant curing groups extending from the second-stage copolymers. Asdiscussed below, these curing groups may react withstep-growth-functional groups present on the first-stage copolymersduring a subsequent curing step.

Preferred glass transition temperatures for the second-stage copolymerinclude those discussed above for the first-stage copolymer. Preferredglass transition temperatures for the overall resulting copolymers ofthe latex emulsion include those greater than about 20° C., morepreferably greater than about 30° C., even more preferably greater thanabout 40° C., and most preferably greater than about 50° C. Preferredglass transition temperatures for the resulting copolymers of the latexemulsion also include those less than about 150° C., more preferablyless than about 140° C., and even more preferably less than about 130°C.

Preferred acid numbers for the resulting copolymer latex (e.g., afterthe second-stage polymerization) include acid numbers greater than about10, more preferably greater than about 20, and even more preferablygreater than about 30 milligrams mg KOH per gram of the copolymer latex.In these embodiments, preferred acid numbers for the resulting copolymerlatex (e.g., after the second-stage polymerization) also include acidnumbers less than about 150, more preferably less than about 140, andeven more preferably less than about 130 mg KOH per gram of thecopolymer latex.

Moreover, preferred amounts of the first-stage monomers, relative to thetotal weight of the first-stage monomers and the second-stage monomers,include amounts greater than 30%, more preferably greater than 40%, andeven more preferably greater than 45% by weight. In some embodiments,preferred amounts of the first-stage monomers, relative to the totalweight of the first-stage monomers and the second-stage monomers, alsoinclude amounts less than 75%, more preferably less than 65%, and evenmore preferably less than 60% by weight.

Preferred amounts of the second-stage monomers, relative to the totalweight of the first-stage monomers and the second-stage monomers,include amounts greater than 25%, more preferably greater than 35%, andeven more preferably greater than 40% by weight. In some embodiments,preferred amounts of the second-stage monomers, relative to thefirst-stage monomers and the second-stage monomers, also include amountsless than 70%, more preferably less than 60%, and even more preferablyless than 55% by weight.

The latex emulsion produced with the above-discussed two-stagepolymerization process may optionally include additional polymerizationstages, if desired. Such additional polymerization stages may occur atany suitable time (e.g., after the second stage, between the first andsecond stages, etc. . . . ). As mentioned above, the first and secondpolymerization stages are example stages for producing the overallresulting copolymers of the latex emulsion, and one or more seedpolymerization stages and/or one or more additional post-polymerizationstages may be used. Preferably, the first and second stage copolymersconstitutes at least about 50% by weight of the resulting copolymers ofthe latex emulsion, more preferably at least about 75% by weight, evenmore preferably at least about 90% by weight, and even more preferablyfrom about 95% to 100% by weight. In some embodiments, the resultingcopolymers of the latex emulsion consist essentially of the first andsecond stage copolymers.

Furthermore, a coating composition may be formulated from the latexemulsion, optionally with the inclusion of one or more additives and/orby rheological modification for different coating applications (e.g.,diluted for spray coating applications). In embodiments in which thecoating composition includes one or more additives, the additivespreferably do not adversely affect the latex emulsion, or a curedcoating formed from the coating composition. For example, such optionaladditives may be included in the coating composition to enhancecomposition esthetics, to facilitate manufacturing, processing,handling, and application of the composition, and to further improve aparticular functional property of the coating composition or a curedcoating resulting therefrom.

Such optional additives include, for example, catalysts, dyes, pigments,toners, extenders, fillers, lubricants, anticorrosion agents, flowcontrol agents, thixotropic agents, dispersing agents, antioxidants,adhesion promoters, light stabilizers, co-resins and mixtures thereof.Each optional additives is preferably included in a sufficient amount toserve its intended purpose, but not in such an amount to adverselyaffect the coating composition or a cured coating resulting therefrom.

One preferred optional additive is a catalyst to increase the rate ofcure. Examples of catalysts, include, but are not limited to, strongacids (e.g., dodecylbenzene sulphonic acid (DDBSA, available as CYCAT600 from Cytec), methane sulfonic acid (MSA), p-toluene sulfonic acid(pTSA), dinonylnaphthalene disulfonic acid (DNNDSA), and triflic acid),quaternary ammonium compounds, phosphorous compounds, and tin and zinccompounds. Specific examples include, but are not limited to, atetraalkyl ammonium halide, a tetraalkyl or tetraaryl phosphonium iodideor acetate, tin octoate, zinc octoate, triphenylphosphine, and similarcatalysts known to persons skilled in the art.

If used, the catalyst is preferably present in an amount of at leastabout 0.01% by weight, and more preferably at least about 0.1% byweight, based on the total solids weight of the coating composition.Furthermore, if used, the catalyst is also preferably present in anamount of no greater than about 3% by weight, and more preferably nogreater than about 1% by weight, based on the total solids weight of thecoating composition.

Another useful optional ingredient is a lubricant (e.g., a wax), whichfacilitates manufacture of metal closures and other fabricated coatedarticles by imparting lubricity to sheets of coated metal substrate.Preferred lubricants include, for example, Carnauba wax andpolyethylene-type lubricants. If used, a lubricant is preferably presentin the coating composition in an amount of at least about 0.1% byweight, and preferably no greater than about 2% by weight, and morepreferably no greater than about 1% by weight, based on the total solidsweight of the coating composition.

Another useful optional ingredient is a pigment, such as titaniumdioxide. If used, a pigment is present in the coating composition in anamount of no greater than about 70% by weight, more preferably nogreater than about 50% by weight, and even more preferably no greaterthan about 40% by weight, based on the total solids weight of thecoating composition.

The above-discussed resulting copolymers of the multi-stagepolymerization process may also be blended with one or more additionallatex copolymers, as desired. In some embodiments, the above-discussedresulting copolymers are greater than about 50% by weight of the blendedlatex emulsion, more preferably greater than about 75%, even morepreferably greater than about 90%, and even more preferably from about95% to 100%, based on an entire weight of latex copolymers in the latexemulsion. In some embodiments, the latex copolymers of the latexemulsion consist essentially above-discussed resulting copolymers.

The latex emulsion may also incorporate one or more optional curingagents (e.g., crosslinking resins, sometimes referred to as“crosslinkers”). The choice of particular crosslinker typically dependson the particular product being formulated. For example, some coatingsare highly colored (e.g., gold-colored coatings). These coatings maytypically be formulated using crosslinkers that themselves tend to havea yellowish color. In contrast, white coatings are generally formulatedusing non-yellowing crosslinkers, or only a small amount of a yellowingcrosslinker. Preferred curing agents are substantially free of BPA, BPF,BPS, glycidyl ether compounds thereof (e.g., BADGE), and epoxy novolacs.

Any of the well known hydroxyl-reactive curing resins can be used. Forexample, phenoplast, blocked isocyanates, and aminoplast curing agentsmay be used, as well as combinations thereof.

Phenoplast resins include the condensation products of aldehydes withphenols. Formaldehyde and acetaldehyde are preferred aldehydes. Variousphenols can be employed such as phenol, cresol, p-phenylphenol,p-tert-butylphenol, p-tert-amylphenol, and cyclopentylphenol.

Aminoplast resins are the condensation products of aldehydes such asformaldehyde, acetaldehyde, crotonaldehyde, and benzaldehyde with aminoor amido group-containing substances such as urea, melamine, andbenzoguanamine. Examples of suitable aminoplast crosslinking resinsinclude benzoguanamine-formaldehyde resins, melamine-formaldehyderesins, esterified melamine-formaldehyde, and urea-formaldehyde resins.One specific example of a suitable aminoplast crosslinker is the fullyalkylated melamine-formaldehyde resin commercially available from CytecIndustries, Inc. under the trade name of CYMEL 303.

As examples of other generally suitable curing agents are the blocked ornon-blocked aliphatic, cycloaliphatic or aromatic di-, tri-, orpoly-valent isocyanates, such as hexamethylene diisocyanate (HMDI),cyclohexyl-1,4-diisocyanate, and the like. Further examples of generallysuitable blocked isocyanates include isomers of isophorone diisocyanate,dicyclohexylmethane diisocyanate, toluene diisocyanate, diphenylmethanediisocyanate, phenylene diisocyanate, tetramethyl xylene diisocyanate,xylylene diisocyanate, and mixtures thereof. In some embodiments,blocked isocyanates are used that have a number-average molecular weightof at least about 300, more preferably at least about 650, and even morepreferably at least about 1,000.

The concentration of the curing agent (e.g., crosslinker) in the coatingcomposition may depend on the type of curing agent, the time andtemperature of the bake, and the molecular weight of the latexcopolymer. If used, the crosslinker is typically present in an amount ofup to about 50% by weight, preferably up to about 30% by weight, andmore preferably up to about 15% by weight. If used, the crosslinker istypically present in an amount of at least about 0.1% by weight, morepreferably at least about 1% by weight, and even more preferably atleast about 1.5% by weight. These weight percentages are based on thetotal solids weight of the coating composition.

In some embodiments, the coating composition may be cured to achievegood crosslinking density without the use of an external crosslinker(e.g., phenolic crosslinkers). Additionally, the coating composition maybe substantially free of formaldehyde and formaldehyde-conditioningmaterials, more preferably essentially free of these compounds, evenmore preferably essentially completely free of these compounds, and mostpreferably completely free of these compounds.

In preferred embodiments, the coating composition is substantially freeor completely free of any structural units derived from bisphenol A(“BPA”), bisphenol F (“BPF”), bisphenol S (“BPS”), or any diepoxidesthereof (e.g., diglycidyl ethers thereof such as the diglycidyl ether ofBPA (“BADGE”)). In addition, the coating composition is preferablysubstantially free or completely free of any structural units derivedfrom a dihydric phenol, or other polyhydric phenol, having estrogenicagonist activity great than or equal to that of4,4′-(propane-2,2-diyl)diphenol. More preferably, the coatingcomposition is substantially free or completely free of any structuralunits derived from a dihydric phenol, or other polyhydric phenol, havingestrogenic agonist activity greater than or equal to that of BPS. Evenmore preferably, the coating composition is substantially free orcompletely free of any structural units derived from a dihydric phenol,or other polyhydric phenol, having estrogenic agonist activity greaterthan 4,4′-(propane-2,2-diyl)bis(2,6-dibromophenol). Optimally, thecoating composition is substantially free or completely free of anystructural units derived from a dihydric phenol, or other polyhydricphenol, having estrogenic agonist activity greater than2,2-bis(4-hydroxyphenyl)propanoic acid. The same is preferably true forany other components of a composition including the coating composition.See, for example, U.S. application Ser. No. 13/570,743 for a discussionof such structural units and applicable test methods.

In some further embodiments, the coating composition is substantiallyfree or completely free of any acrylamide-type monomers (e.g.,acrylamides or methacrylamide). Moreover, in some embodiments, thecoating composition is substantially free or completely free of styrene(whether free or polymerized). As discussed above, in these embodiments,the first-stage monomers and/or the second-stage monomers may includeother ethylenically-unsaturated aromatic compounds and/orethylenically-unsaturated alicyclic compounds, such as aromatic(meth)acrylates and/or alicyclic (meth)acrylates, for example. Inadditional further embodiments, the coating composition is substantiallyfree or completely free of halogenated monomers (whether free orpolymerized), such as chlorinated vinyl monomers.

The coating composition may also optionally be rheologically modifiedfor different coating applications. For example, the coating compositionmay be diluted with additional amounts of the aqueous carrier to reducethe total solids content in the coating composition. Alternatively,portions of the aqueous carrier may be removed (e.g., evaporated) toincrease the total solids content in the coating composition. The finaltotal solids content in the coating composition may vary depending onthe particular coating application used (e.g., spray coating), theparticular coating use (e.g., for interior can surfaces), the coatingthickness, and the like.

In some embodiments, the coating composition preferably has a totalsolids content greater than about 5%, more preferably greater than about10%, and even more preferably greater than about 15%, based on the totalweight of the coating composition. The coating composition alsopreferably has a total solids content less than about 80%, morepreferably less than about 60%, and even more preferably less than about50%, based on the total weight of the coating composition. The aqueouscarrier may constitute the remainder of the weight of the coatingcomposition.

In some embodiments, such as for certain spray coating applications(e.g., inside spray for food or beverage cans), the coating compositionmay have a total solids content greater than about 5%, more preferablygreater than about 10%, and even more preferably greater than about 15%,based on the total weight of the coating composition. In theseembodiments, the coating composition may also have a total solidscontent less than about 40%, more preferably less than about 30%, andeven more preferably less than about 25%, based on the total weight ofthe coating composition. In some of these embodiments, the coatingcomposition may have a total solids content ranging from about 18% toabout 22%. The aqueous carrier may constitute the remainder of theweight of the coating composition.

The coating composition preferably includes at least a film-formingamount of the latex emulsion copolymers of the present disclosure. Assuch, the latex emulsion copolymers preferably constitute greater thanabout 50%, more preferably greater than about 65%, and even morepreferably greater than about 80% by weight of the coating composition,based on an entire weight of the total solids in the coatingcomposition. The latex emulsion copolymers may constitute 100% or less,more typically less than about 99%, and even more typically less thanabout 95% by weight of the coating composition, based on the entireweight of the total solids in the coating composition.

As previously discussed, the aqueous carrier of the coating compositionpreferably includes water and may further include one or more optionalorganic solvents. In some embodiments, water constitutes greater thanabout 20% by weight, more preferably greater than about 35% by weight,and even more preferably greater than about 50% by weight of the totalweight of the aqueous carrier. In some embodiments, water constitutes100% or less, more preferably less than about 95% by weight, and evenmore preferably less than about 90% by weight of the total weight of theaqueous carrier.

While not intending to be bound by theory, the inclusion of a suitableamount of an organic solvent can be advantageous, in some embodiments(e.g., for certain coil coating applications to modify flow and levelingof the coating composition, control blistering, and maximize the linespeed of the coil coater). Accordingly, in certain embodiments, theorganic solvents may constitute greater than 0%, more preferably greaterthan about 5%, and even more preferably greater than about 10% by weightof the aqueous carrier, based on the total weight of the aqueouscarrier. In these embodiments, the organic solvents may also constituteless than about 60%, more preferably less than about 50%, and even morepreferably less than about 40% by weight of the aqueous carrier, basedon the total weight of the aqueous carrier.

The coating composition preferably has a viscosity suitable for a givencoating application. In some embodiments, such as for certain spraycoating applications (e.g., those discussed below for FIGS. 2 and 3),the coating composition may have an average viscosity greater than about30 seconds, more preferably greater than 40 seconds, and even morepreferably greater than about 45, based on the Viscosity Test describedbelow. In some embodiments, the coating composition may also have anaverage viscosity less than about 90 seconds, more preferably less than80 seconds, and even more preferably less than about 75, based on theViscosity Test described below.

The coating composition of the present disclosure having the emulsionpolymerized latex copolymers may be applied to a variety of differentsubstrates using a variety of different coating techniques. As brieflydescribed above, cured coatings formed from the coating composition areparticularly suitable for use on food and beverage cans (e.g., two-piececans, three-piece cans, and the like). Two-piece cans are typicallymanufactured by a drawn and ironing (“D&I”) process. The cured coatingsare also suitable for use in food or beverage contact situations, andmay be used on the inside or outside of such cans.

For instance, FIG. 1 shows container 20, which is a simplified exampleof a food or beverage container that may be coated with the coatingcomposition of the present disclosure. Container 20 may be a two-piececan having body 22 and lid piece 24, where body 22 includes sidewall 26and bottom end 28. Lid piece 24 may be sealed to body 22 in any suitablemanner, and may optionally include one or more tabs (not shown) tofacilitate peeling off or opening of lid piece 24 or a portion thereof(e.g., as is common for beverage can ends and easy-open food can ends).

Sidewall 26 and bottom end 28 respectively include interior surfaces 30and 32, and suitable substrate materials for sidewall 26 and bottom end28 include metallic materials, such as aluminum, iron, tin, steel,copper, and the like. One or more portions of interior surfaces 30 and32 may be coated with coating 34, which is a cured coating formed fromthe latex emulsion of the present disclosure. In some embodiments, theinterior surface of lid piece 24 may also be coated with coating 34.Alternatively, in some embodiments, the interior surface of lid piece 26may be coated with coating 34, and interior surfaces 30 and 32 may becoated with other coating materials.

Furthermore, the coating composition is particularly suitable for sprayapplications for interior surfaces, such as the interior surfaces offood cans, beer and beverage containers, and the like. For example, thecoating composition is particularly suitable for spray applications ontothe interior surfaces (e.g., interior surfaces 30 and 32) of two-piecefood or beverage cans (e.g., drawn and ironed beverage cans, which aretypically made of steel or aluminum substrate).

A suitable spray coating technique for applying the coating compositionto an interior surface of a food or beverage can may involve sprayingthe coating composition using a spray nozzle capable of uniformlycoating the inside of the can. For example, FIG. 2 illustrates a sideview, and FIG. 3 illustrates a top view of an example setup for spraycoating the coating composition onto the interior surfaces 30 and 32 ofa can 20 with a spray nozzle 36. As shown, the spray nozzle 36 ispreferably a controlled-pattern nozzle capable of generating a desiredspray pattern, such as spray 38 having a flat-fan pattern as generallyillustrated in FIGS. 2 and 3.

Furthermore, spray nozzle 36 is preferably stationary, and alsopreferably generates spray 38 without air pressure (e.g., an airlessspray operation). In some embodiments (e.g., in which the can to besprayed is large), spray nozzle 36 may utilize a “lance spray”technique, where spray nozzle 36 may move relative to the can to reachthe far inside end of the can.

In addition, the can 20 itself may be engaged to a rotating mechanism(e.g., a drive roller or belt, and/or a rotatable chuck mount), which isconfigured to rotate the can 20 at a high speed (e.g., about 2,200 rpm)around its longitudinal axis 40, as illustrated by arrows 42. Thisrotation of the can 20 preferably spreads the sprayed coatingcomposition evenly across the entire interior surfaces 30 and 32. As canbe seen in FIG. 2, the flat-fan pattern of spray 38 is not evenlyaligned with the longitudinal axis 40 of the can 20. As such, thepattern of spray 38, as dictated by spray nozzle 36, may benon-homogenous, where the lower portion of spray 38 has a greaterdensity of the coating composition compared to the upper portion ofspray 38.

After the spray coating application, each can 20 may be moved to acuring oven to cure the sprayed coating composition, which is preferablyperformed within about 40 to 200 seconds from the spraying step. Thecuring process is preferably performed in bulk with multiple cans 20arranged together on a continuously moving conveyor belt or track. Thecuring oven preferably heats the cans 20 to a suitable temperature tocure the coating composition, but that is also preferably not too highso as to degrade the coating composition, any other existing coatings oncans 20, and/or the metal materials of cans 20.

Suitable curing temperatures for the coating composition of the presentdisclosure are greater than about 150° C. (about 300° F.), morepreferably greater than about 165° C. (about 330° F.), and even morepreferably greater than about 360° F. In some embodiments, suitablecuring temperatures for the coating composition of the presentdisclosure are also less than about 220° C. (about 430° F.), morepreferably less than about 205° C. (about 400° F.), and even morepreferably less than about 195° C. (about 380° F.). These temperaturesare based on peak metal temperature measurements of the metal walls ofthe cans 20 as they pass through the curing oven. For example, multiplecans 20 may be grouped together with a test can that is wired withthermocouples to measure the temperatures of one or more portions of themetal walls to ensure the cans 20 are heated enough.

Suitable residence times in the curing oven for the above-discussedtemperatures range from about 40 seconds to about three minutes, morepreferably about one minute to about two minutes. After curing, theresulting cured coatings (e.g., coating 34) may have suitable filmthicknesses for protecting the cans 20 from food or beverage productsthat are subsequently filled into the cans 20.

The desired film thickness for the cured coating may vary depending onthe particular food or beverage to be filled in a given can 20. In someembodiments for the spray coating application (e.g., inside spray forfood or beverage cans), the average film thickness after curing isgreater than about 0.7 milligrams/square-inch (mg/inch²), morepreferably greater than about 0.8 mg/inch², and even more preferablygreater than about 0.9 mg/inch². In these embodiments, the average filmthickness after curing is also less than about 4.0 mg/inch², morepreferably less than about 3.0 mg/inch², and even more preferably lessthan about 2.5 mg/inch².

In some further embodiments, the average film thickness after curingranges from about 0.9 mg/inch² to about 1.1 mg/inch². In other furtherembodiments, the average film thickness after curing ranges from about1.4 mg/inch² to about 1.6 mg/inch². In yet other further embodiments,the average film thickness after curing ranges from about 1.9 mg/inch²to about 2.1 mg/inch².

Alternatively, the coating composition may applied as a coil coating.During a coil coating application, a continuous coil composed of a metal(e.g., steel or aluminum) is coated with the coating composition of thepresent disclosure. Once coated, the coating coil may be subjected to ashort thermal, ultraviolet, and/or electromagnetic curing cycle, forhardening (e.g., drying and curing) of the coating composition. Coilcoatings provide coated metal (e.g., steel and/or aluminum) substratesthat can be fabricated into formed articles, such as two-piece drawnfood cans, food can ends, drawn and ironed cans, beverage can ends, andthe like.

The coating composition of the present disclosure also offers utility inother coating applications. These additional applications include, butare not limited to, wash coating, sheet coating, and side seam coatings(e.g., food can side seam coatings).

Other commercial coating application and curing methods are alsoenvisioned, for example, electrocoating, extrusion coating, laminating,powder coating, and the like. The coating composition may also be usefulin medical or cosmetic packaging applications, including, for example,on surfaces of metered-dose inhalers (“MDIs”), including on drug-contactsurfaces.

During the above-discussed curing steps, the aqueous carrier ispreferably vaporized or otherwise dried off from the emulsionpolymerized copolymers, allowing them to cure. If desired, the dryingand curing steps may be combined in a single step or carried out inseparate steps.

In some embodiments, the coating composition may be cured with goodcrosslinking density without the use of an external crosslinker. Forexample, after curing, preferred coatings produced from the coatingcomposition of the present disclosure without an external crosslinkermay withstand more than 100 double rubs, and more preferably greaterthan 200 double rubs, based on the Solvent Resistance test discussedbelow.

Even more preferably, the cured coatings exhibit combinations of theabove properties, including the Solvent Resistance test results, theMetal Exposure after Drop Damage test results, the Corrosion Resistancetest results, and the flexibility results. In certain preferredembodiments, this is in additional to being suitable for use in spraycoating applications to form spray coatings on interior can surfaces.Accordingly, the coating composition of the present disclosure isparticularly suitable for use as food and beverage-contact coatings incontainers (or portions thereof) configured retain a variety ofdifferent food or beverage products.

Property Analysis a3nd Characterization Procedures

Various properties and characteristics of the latex emulsions, coatingcompositions, and coatings described herein may be evaluated by varioustesting procedures as described below:

1. Curing Conditions

For beverage inside spray bakes, the curing conditions involvemaintaining the temperature measured at the can dome at 188° C. to 210°C. for 60 seconds. For beverage end coil bakes, the curing conditionsinvolve the use of a temperature sufficient to provide a peak metaltemperature within the specified time (e.g., 10 seconds at 204° C. means10 seconds, in the oven, for example, and a peak metal temperatureachieved of 204° C.). The constructions cited were evaluated by tests asfollows.

2. Solvent Resistance

The extent of cure or crosslinking of a coating is measured as aresistance to methyl ethyl ketone (MEK, available from Exxon, Newark,N.J.). This test is performed as described in ASTM D 5402-93. The numberof double-rubs (i.e., one back- and forth motion) is reported.

3. Adhesion

Adhesion testing is performed to assess whether the coating adheres tothe coated substrate. The adhesion test was performed according to ASTMD 3359—Test Method B, using SCOTCH 610 tape, available from 3M Companyof Saint Paul, Minn. Adhesion is generally rated on a scale of 0-10where a rating of “0” indicates no adhesion failure (best), a rating of“1” indicates 90% of the coating remains adhered, a rating of “2”indicates 80% of the coating remains adhered, and so on. Adhesionratings of 0 are typically desired for commercially viable coatings.

4. Blush Resistance

Blush resistance measures the ability of a coating to resist attack byvarious solutions. Typically, blush is measured by the amount ofsolution (e.g., water) absorbed into a coated film. When the filmabsorbs water, it generally becomes cloudy or looks white. Blush isgenerally measured visually using a scale of 0-10 where a rating of “0”indicates no blush (best) and a rating of “10” indicates completewhitening of the film (worst). Blush ratings of 3 or less are typicallydesired for commercially viable coatings, and optimally 1 or less.

5. Blush Adhesion Resistance

Blush Adhesion Resistance is a combination of adhesion resistance andblush resistance results as described above for the Adhesion test andthe Bush Resistance test.

6. Corrosion Resistance

These tests measure the ability of a coating to resist attack bysolutions of different levels of aggressiveness. Briefly, a givencoating is subjected to a particular solution, as described below, andthen measured for adhesion and blush resistance, each also describedbelow. For each test, a result is given using a scale of 0-10, based onthe adhesion and blush resistance, where a rating of “0” is best and arating of “10 is worst. Commercially viable beverage interior coatingspreferably give adhesion ratings of 0 and blush ratings of less than 3,optimally less than 1, in the given solutions tested.

A. Deionized Water

Deionized water is heated to 82° C. Coated panels are immersed in theheated solution for 30 minutes and then removed, rinsed, and dried.Samples are then evaluated for adhesion and blush, as previouslydescribed.

B. Joy Detergent Solution

A 1% solution of JOY Detergent (available from Procter & Gamble) indeionized water is prepared and heated to 82° C. Coated panels areimmersed in the heated solution for 10 minutes and then removed, rinsed,and dried. Samples are then evaluated for adhesion and blush, aspreviously described.

C. Acetic Acid Solution

A 3% solution of acetic acid (C2H402) in deionized water is prepared andheated to 100° C. Coated panels are immersed in the heated solution for30 minutes and then removed, rinsed, and dried. Samples are thenevaluated for adhesion and blush, as previously described.

D. Citric Acid Solution

A 2% solution of citric acid (C6H807) in deionized water is prepared andheated while subjected to a pressure sufficient to achieve a solutiontemperature of 121° C. Coated panels are immersed in the heated solutionfor 30 minutes and then removed, rinsed, and dried. Samples are thenevaluated for adhesion and blush, as previously described.

E. Cider Solution

A cider solution of 32.4 grams/liter malic acid. 9.6 grams/liter lacticacid, 12.9 grams/liter acetic acid, and 125 milligrams/liter sodiumsulfite is prepared and heated to 37° C. Coated panels are immersed inthe heated solution for 24 hours and then removed, rinsed, and dried.Samples are then evaluated for adhesion and blush, as previouslydescribed.

7. Crazing-Reverse Impact Resistance (RIR)

The reverse impact measures the coated substrate's ability to withstandthe deformation encountered when impacted by a steel punch with ahemispherical head. For the present evaluation, coated substrate wassubjected to 12 in-lbs (1.36 N m) of force using a BYK-Gardner “overall”Bend and Impact Tester and rated visually for micro-cracking ormicro-fracturing commonly referred to as crazing. Test pieces wereimpacted on the uncoated or reverse side. A rating of 0 indicates nocraze and suggests sufficient flexibility and cure. A rating of 10indicates complete failure. Commercially viable coatings preferably showslight or no crazing on a reverse impact test.

8. Impact on Dome

Dome impact was evaluated by subjecting the dome apex of a 12-ouncebeverage can to a reverse impact as described in the previous section.Craze was evaluated after impact. A rating of 0 indicates no craze andsuggests sufficient flexibility and cure. A rating of 10 indicatescomplete failure. Coatings for beverage can interiors preferably show nocraze (rating of 0) on a dome impact test.

9. Wedge-Bend

This is a flexibility test for a coating, and correlates to how acoating will withstand a can formation process (e.g., necking steps).Test coatings are applied to a suitable panel and cured. The coatedpanel is then bent around a 5-millimeter diameter metal rod having a15-centimeter length. The bent panel is then flattened with a 2,400-gramhammer along its length with a folding height ranging between zeromillimeters and six millimeters. The resulting panel is then immersed ina 10% hydrochloric acid (provided at a 36% concentration)/coppersulphate solution for a 3-minute duration. The corrosion is then ratedby measuring the wedge bend length corroded and expressed in % ofunaltered coating.

10. Metal Exposure after Drop Damage

Drop damage resistance measures the ability of the coated container toresist cracks after being in conditions simulating dropping of a filledcan. The presence of cracks is measured by passing electrical currentvia an electrolyte solution, as previously described in the MetalExposure section. A coated container is filled with the electrolytesolution and the initial metal exposure is recorded. The can is thenfilled with water and dropped through a tube from a 14-centimeter heightonto an inclined plane, causing a dent in the chime area. The can isthen turned 180 degrees, and the process is repeated.

Water is then removed from the can and metal exposure is again measuredas described above. If there is no damage, no change in current (mA)will be observed. Typically, an average of 6 or 12 container runs isrecorded. The metal exposures results for before and after the drop arereported as absolute values. The lower the milliamp value, the betterthe resistance of the coating to drop damage. Preferred coatings givemetal exposure values after drop damage of less than 3.5 mA, morepreferred values of less than 2.5 mA, and even more preferred values ofless than 1.5 mA.

11. Sterilization or Pasteurization

The sterilization or pasteurization test determines how a coatingwithstands the processing conditions for different types of foodproducts packaged in a container. Typically, a coated substrate isimmersed in a water bath and heated for 5-60 minutes at temperaturesranging from 65° C. to 100° C. For the present evaluation, the coatedsubstrate was immersed in a deionized water bath for 45 minutes at 85°C. The coated substrate was then removed from the water bath and testedfor coating adhesion and blush as described above. Commercially viablecoatings preferably provide adequate pasteurization resistance withperfect adhesion (rating of 0) and blush ratings of 5 or less, optimally1 or less.

12. Process or Retort Resistance

This is a measure of the coating integrity of the coated substrate afterexposure to heat and pressure with a liquid such as water. Retortperformance is not necessarily required for all food and beveragecoatings, but is desirable for some product types that are packed underretort conditions. The procedure is similar to the Sterilization orPasteurization test. Testing is accomplished by subjecting the substrateto heat ranging from 105-130° C. and pressure ranging from 0.7 to 1.05kilograms/square-centimeter for a period of 15 to 90 minutes.

For the present evaluation, the coated substrate is immersed indeionized water and subjected to heat of 121° C. (250° F.) and pressureof 1.05 kilograms/square-centimeter for a period of 90 minutes. Thecoated substrate is then tested for adhesion and blush as describedabove. In food or beverage applications requiring retort performance,adhesion ratings of 0 and blush ratings of 3 or less are typicallydesired for commercially viable coatings.

13. Global Extractions

The global extraction test is designed to estimate the total amount ofmobile material that can potentially migrate out of a coating and intofood packed in a coated can. Typically coated substrate is subjected towater or solvent blends under a variety of conditions to simulate agiven end use. Acceptable extraction conditions and media can be foundin 21 CFR § 175.300 paragraphs (d) and (e). The allowable globalextraction limit as defined by the FDA regulation is 50 parts permillion (ppm).

The extraction procedure used in the current invention is described in21 CFR § 175.300 paragraph (e)(4)(xv) with the following modificationsto ensure worst-case scenario performance: (1) the alcohol (ethanol)content was increased to 10% by weight, and (2) the filled containerswere held for a 10-day equilibrium period at 37.8° C. (100° F.). Theseconditions are per the FDA publication “Guidelines for Industry” forpreparation of Food Contact Notifications.

The coated beverage can is filled with 10% by weight aqueous ethanol andsubjected to pasteurization conditions (65.6° C., 150° F.) for 2 hours,followed by a 10-day equilibrium period at 37.8° C. (100° F.).Determination of the amount of extractives is determined as described in21 CFR § 175.300 paragraph (e) (5), and ppm values were calculated basedon surface area of the can (no end) of 44 square inches with a volume of355 milliliters. Preferred coatings give global extraction results ofless than 50 ppm, more preferred results of less than 10 ppm, even morepreferred results of less than 1 ppm. Most preferably, the globalextraction results are optimally non-detectable.

14. Initial Metal Exposure

This test method determines the amount of the inside surface of the canthat has not been effectively coated by the sprayed coating. Thisdetermination is made through the use of an electrically conductivesolution (1% NaCl in deionized water). The coated can is filled withthis room-temperature conductive solution, and an electrical probe isattached in contact to the outside of the can (uncoated, electricallyconducting). A second probe is immersed in the salt solution in themiddle of the inside of the can.

If any uncoated metal is present on the inside of the can, a current ispassed between these two probes and registers as a value on an LEDdisplay. The LED displays the conveyed currents in milliamps (mA). Thecurrent that is passed is directly proportional to the amount of metalthat has not been effectively covered with coating. The goal is toachieve 100% coating coverage on the inside of the can, which wouldresult in an LED reading of 0.0 mA. Preferred coatings give metalexposure values of less than 3 mA, more preferred values of less than 2mA, and even more preferred values of less than 1 mA. Commerciallyacceptable metal exposure values are typically less than 2.0 mA onaverage.

15. Viscosity Test

This test measures the viscosity of a latex emulsion or coatingcomposition for rheological purposes, such as for sprayability and othercoating application properties. The test was performed pursuant to ASTMD1200-88 using a Ford Viscosity Cup #2 at 80° F. The results aremeasured in the units of seconds.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art. The following Table 1lists some of the raw materials used in the following examples.Alternative materials or suppliers may be substituted as is appreciatedto one skilled in the art.

TABLE 1 Raw Material Trade Name Supplier Polyermizable SurfactantREASOAP Adeka Corporation, Monomer SR1025 Tokyo, Japan Organic AcidCatalyst, CYCAT 600 Cyctec Industries, Inc., 25% in ammonia WoodlandPark, NJ Ammonium Persulphate Sigma-Aldrich Co. LLC, St. Louis, MOStyrene Rohm & Haas, Philadelphia, PA Methacrylic Acid Rohm & Haas,Philadelphia, PA Ethyl Acrylate Rohm & Haas, Philadelphia, PAHydroxyethyl Methacrylate Rohm & Haas, (HEMA) Philadelphia, PA ButylGlycol The DOW Chemical Co., Midland, MI Dimethylethanol Amine BASF SE,(DMEA) Ludwigshafen, Germany Glycidyl Methacrylate Rohm & Haas, (GMA)Philadelphia, PA Ferrous Sulphate Sigma-Aldrich Co. LLC, HeptahydrateSt. Louis, MO Tertioamyl Hydroperoxide TAH 85 Arkema, Inc., Colombes,France Isoabscorbic Acid Sigma-Aldrich Co. LLC, St. Louis, MO

Coating Composition CC1

A coating composition CC1 was prepared using the above-discussedtwo-stage polymerization process. For the first-stage polymerization,790 parts of deionized water, 18 parts of the polymerizable surfactantmonomer, and 10.2 parts of the organic acid catalyst were added to areactor equipped, which was then heated under nitrogen sparge to 80° C.with agitation. Once equilibrium temperature was reached, an initiatorsolution and the first-stage monomers were introduced to the surfactantdispersion in the reactor continuously over a 75-minute duration whilethe reactor was maintained under nitrogen sparge at the temperature of80° C. with agitation.

The initiator solution included 0.5 parts of ammonium persulphate and 40parts of deionized water. The first-stage monomers included 144 partsstyrene, 55 parts methacrylic acid, 37 parts ethyl acrylate, and 27parts hydroxyethyl methacrylate (HEMA), which were carried in 20 partsof a buytl glycol solvent. After all of the initiator solution and thefirst-stage monomers were added, the reactor was held at the temperatureof 80° C. under agitation for an additional 30 minutes to complete thefirst-stage emulsion polymerization, thereby producing an in situ latexemulsion having the first-stage copolymers. These first-stage copolymersincluded chain segments of the polymerizable surfactant monomer, andcarboxylic acid groups.

A portion of the carboxylic acid groups of the resulting first-stagecopolymers were then neutralized for water-dispersibility purposes. Thisincluded introducing 2.85 parts of dimethylethanol amine (DMEA) and 40parts of deionized water over a period of 30 minutes. Then, after 15additional minutes, a redox solution was introduced to the reactor,which included 0.001 parts of ferrous sulphate heptahydrate, 0.32 partsof tertioamyl hydroperoxide, and 10 parts of deionized water. Then asecond initiator solution and the second-stage monomers were introducedto the reactor continuously over a 75-minute duration while the reactorwas maintained under nitrogen sparge at the temperature of 80° C. withagitation.

The second initiator solution included 0.24 parts of isoabscorbic acidand 40 parts of deionized water. The second-stage monomers included 144parts styrene, 55 parts glycidyl methacrylate (i.e., for the curingchains), 42 parts ethyl acrylate, and 11 parts hydroxyethyl methacrylate(HEMA), which were carried in 30 parts of a buytl glycol solvent.

After all of the second initiator solution and the second-stage monomerswere added, the reactor was held at the temperature of 80° C. underagitation for an additional 30 minutes. Then a spike of the initiatorand redox solutions was added to reduce the level of free monomers. Thespike included 0.001 parts of ferrous sulphate heptahydrate, 0.3 partsof tertioamyl hydroperoxide, 0.2 parts of isoabscorbic acid, and 10parts of deionized water. The reactor was maintained under nitrogensparge at the temperature of 80° C. with agitation for an additional 90minutes to complete the second-stage emulsion polymerization, therebyproducing a latex emulsion having first-stage copolymers andsecond-stage copolymers, which were not linked via linkage chains. Thesecond-stage copolymers, however, included curing chains with pendentoxirane groups for a subsequent curing step.

After the second-stage polymerization was completed, the reactor wasslowly cooled down to 40° C. and filtered to collect the resulting latexemulsion, where no coagulum was visibly observable. The resulting latexemulsion had a total solids content of 31.8% by weight, an acid numberof 66 mg KOH per gram of the resulting latex emulsion copolymers, aviscosity of 15 seconds based on the Viscosity Test, and a pH of 6.9.The resulting latex emulsion copolymers included monomer concentrationsas listed below in Table 2.

TABLE 2 Percent by weight First-Stage Monomers and Linkage MonomersPolyermizable Surfactant Monomer 6.4 Styrene 51.2 Methacrylic Acid 19.6Ethyl Acrylate 13.2 Hydroxyethyl Methacrylate (HEMA) 9.6 LinkageMonomers 0.0 Second-Stage Monomers Styrene 57.1 Glycidyl Methacrylate(GMA) 21.8 Ethyl Acrylate 16.7 Hydroxyethyl Methacrylate (HEMA) 4.4Total Monomers First-Stage Monomers 52.7 Linkage Monomers 0.0Second-Stage Monomers 47.3

The resulting latex emulsion was then diluted with a solution ofdeionized water and organic solvents to reach a viscosity between 15 and25 seconds based on the Viscosity Test. This resulted in the coatingcomposition CC1, which did not included any external crosslinker.

The coating composition CC1 was applied to flat aluminum and steelpanels with an applied coating thickness of 4 grams/square-meter. Eachapplied coating composition was then cured for 60 seconds at atemperature of 193° C. to produce cured coatings. Each coating was thenevaluated for use as an internal surface-coating for two-piece beveragecans, with involved subjecting the coating to corrosion resistance testsin different solutions, solution stability tests, and reverse impactcrazing tests.

A. Solvent Resistance Testing

The applied and cured coatings for coating composition CC1 was subjectedto a Solvent Resistance test to determine their extents of crosslinking.Comparative coatings produced from an epoxy-based coating compositionwere also tested for comparison. Table 3 lists the Solvent Resistancetest results for the coating composition CC1 and the epoxy-based controlfor (i) initial coatings, and (ii) coatings aged for one month at 50°C., where the results are in a number of double rubs.

TABLE 3 Solution Stability Test Solution Stability Test CoatingComposition Results (Initial) Results (Aged) Coating Composition 240 230CC1 Epoxy control 120 120

As shown in Table 3, the coating composition CC1 exhibited goodcrosslinking without requiring the use of an external crosslinker, andexceeded the results of the epoxy control. Furthermore, the coatingcomposition CC1 maintained the ability to generate good crosslinkingeven after the aging conditions. This illustrates the good curingstability of this coating composition.

B. Corrosion Resistance Testing

The applied and cured coatings for coating composition CC1 were alsosubjected to various corrosion resistance tests pursuant to theabove-described procedures for deionized water, the Joy detergentsolution, the acetic acid solution, the citric acid solution, and thecider solution. A comparative coating produced from an epoxy-basedcoating composition were also tested for comparison. Table 4 lists theBlush Adhesion Resistance results for the coating composition CC1 andthe epoxy-based control.

TABLE 4 Coating Corrosion Test Solution Composition CC5 Epoxy controlDeionized Water 0 0 Joy Detergent Solution 0 0 Acetic Acid Solution 4 0Citric Acid Solution 2 0 Cider Solution 1 0

As shown in Table 4, the coatings exhibited suitable corrosionresistance, particularly to the less-aggressive solutions. As such, thecoating composition CC1 may be used in a variety of such food andbeverage environments.

C. Crazing Reverse Impact Resistance (RIR) Testing

The applied and cured coatings for coating composition CC1 were alsosubjected to the Crazing RIR testing, as described above, to measure thecoated substrate's ability to withstand the deformation encountered whenimpacted by a steel punch with a hemispherical head. Table 5 lists theCrazing RIR test results for the coating composition CC1 and theepoxy-based control for (i) initial coatings, and (ii) uncured coatingcompositions aged for 15 days at 50° C. (and then applied and curedbefore testing).

TABLE 5 Crazing RIR Crazing RIR Coating Composition (Initial) (15 Days)Coating Composition CC1 0 3 Epoxy control 0 0

As shown in Table 5, the coating compositions exhibited good impactresistance.

Coating Compositions CC2 and CC3

Coating compositions CC2 and CC3 were prepared using the above-discussedtwo-stage polymerization process as used to produce the coatingcomposition CC1. However, the coating compositions CC2 and CC3 did notinclude any polymerizable or non-polymerizable surfactant. Instead,these coating compositions illustrate how the first-stage monomers andthe second-stage monomers may be sufficiently dispersed in an aqueouscarrier without the use of separate surfactants to undergo emulsionpolymerization processes.

For both coating compositions CC2 and CC3, the ammonium persulphatesufficiently dispersed the first-stage monomers and the second-stagemonomers, and the resulting copolymers, in the aqueous carrier withoutthe use of separate surfactants. After polymerization, the resultinglatex copolymers were then neutralized to assist in maintaining waterdispersibiltiy.

For the coating composition CC2, the resulting latex emulsion had atotal solids content of 34.4% by weight, an acid number of 73.8 mg KOHper gram of the resulting latex emulsion copolymers, and a calculatedglass transition temperature of 54° C. For the coating composition CC3,the resulting latex emulsion had a total solids content of 34.6% byweight, an acid number of 71.9 mg KOH per gram of the resulting latexemulsion copolymers, and a calculated glass transition temperature of43° C. The resulting latex emulsion copolymers included monomerconcentrations as listed below in Tables 6 and 7, respectively.

TABLE 6 Percent by weight First-Stage Monomers and Linkage MonomersSurfactant 0.0 Ethyl Acrylate 40.9 Styrene 40.9 Methacrylic Acid 18.2Second-Stage Monomers Styrene 66.7 Glycidyl Methacrylate (GMA) 11.1Ethyl Acrylate 22.2 Total Monomers First-Stage Monomers 55.0Second-Stage Monomers 45.0

TABLE 7 Percent by weight First-Stage Monomers and Linkage MonomersSurfactant 0.0 Ethyl Acrylate 54.5 Styrene 27.3 Methacrylic Acid 18.2Second-Stage Monomers Styrene 66.7 Glycidyl Methacrylate (GMA) 11.1Ethyl Acrylate 22.2 Total Monomers First-Stage Monomers 55.0Second-Stage Monomers 45.0

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference to the extentthat they do not conflict with the present disclosure. Although thepresent disclosure has been described with reference to preferredembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the disclosure.

1-25. (canceled)
 26. An interior can coating composition including atleast 50 weight percent, based on the weight of total solids in thecoating composition, of a latex-based acrylic coating compositionincluding a latex emulsion that is a reaction product of a methodcomprising: emulsion polymerizing first-stage monomers in an aqueouscarrier to produce a first-stage copolymer comprising water dispersinggroups, wherein the first-stage monomers include greater than 3% byweight of step-growth-functional monomers having step-growth-functionalgroups, based on an entire weight of the first-stage monomers; andemulsion polymerizing second-stage monomers in the presence of thefirst-stage copolymer to form a second-stage copolymer, wherein thesecond-stage copolymer is chemically different from the first-stagecopolymer, and wherein the second-stage copolymer comprises a curinggroup configured to react with one of the step-growth-functional groupsof the first-stage copolymer during a curing step; wherein the coatingcomposition is substantially free of structural units derived from eachof (meth)acrylamide-type monomers and bisphenol A.
 27. The coatingcomposition of claim 26, wherein the coating composition is an insidespray beverage can coating composition having a viscosity ranging fromabout 45 seconds to about 75 seconds, based on the Viscosity Testdescribed herein.
 28. The coating composition of claim 26, wherein thecoating composition, when spray applied onto an interior of an aluminumbeverage can and cured at 188 ° C. to 210 ° C. (measured at the candome) for 60 seconds to provide a coating with an average film thicknessof about 0.7 mg/in² to about 4.0 mg/in², exhibits a global extractionresult of less than 50 ppm as measured according to the extractionprocedure in 21 C.F.R. §175.300, paragraphs (d)-(e).
 29. The coatingcomposition of claim 26, wherein the first-stage emulsion polymerizedlatex copolymer comprises greater than about 10% by weight of themonomer units having the step-growth-functional groups.
 30. The coatingcomposition of claim 26, wherein the step-growth-functional groupscomprise acid-functional groups, alcohol-functional groups,amine-functional groups, or combinations thereof.
 31. The coatingcomposition of claim 26, wherein the step-growth-functional groupscomprise acid-functional groups, and wherein the acid-functional groupscomprise carboxylic acid-functional groups, anhydrides thereof, saltsthereof, or combinations thereof; and wherein the first-stage emulsionpolymerized latex copolymer has an acid number of greater than 40 mg KOHper gram of the first-stage copolymer.
 32. The coating composition ofclaim 26, wherein the first-stage copolymer has an acid number greaterthan about 80 milligrams potassium hydroxide per gram of first-stagecopolymer.
 33. The coating composition of claim 26, wherein thefirst-stage monomers comprise one or more polymerizable surfactantmonomers.
 34. The coating composition of claim 26, wherein emulsionpolymerizing the first-stage monomers is performed without the use ofany polymerizable or non-polymerizable surfactants.
 35. The coatingcomposition of claim 26, wherein the second-stage copolymer furthercomprises at least one functional group comprising an oxirane group, anisocyanate group, an azlactone group, an oxazoline group, acyclocarbonate group, or a combination thereof.
 36. The coatingcomposition of claim 26, wherein the curing group comprises an oxiranegroup, and wherein the second-stage monomers comprise glycidylmethacrylate.
 37. The coating composition of claim 36, whereinsecond-stage monomers comprise greater than 5% to less than 30% byweight of glycidyl methacrylate.
 38. The coating composition of claim26, wherein the second-stage monomers are, when considered overall, morehydrophobic relative to those of the first-stage copolymer.
 39. Thecoating composition of claim 26, wherein the coating composition issubstantially free of structural units derived from either bisphenol For bisphenol S, and wherein the coating composition is substantiallyfree of formaldehyde or formaldehyde-forming materials.
 40. The coatingcomposition of claim 26, wherein the coating composition issubstantially free of styrene.
 41. The coating composition of claim 26,wherein the first-stage copolymer has a glass transition temperature ofgreater than 30° C. and wherein the second-stage copolymer has a glasstransition temperature of greater than 30° C., and wherein thefirst-stage monomers are present in an amount greater than 0% by weightto less than 75% by weight relative to the total weight of first-stagemonomers and second-stage monomers.
 42. The coating composition of claim26, wherein after curing, the coating composition, without an externalcrosslinker, withstands more than 100 double rubs when tested accordingto the Solvent Resistance Test described herein.
 43. The coatingcomposition of claim 26, wherein the coating composition comprises aphenoplast crosslinker.
 44. An inside spray beverage can coatingcomposition having a total solids content of greater than about 15% toless than about 25%, and including at least 50 weight percent, based onthe weight of total solids in the coating composition, of a latexemulsion that is a reaction product of a method comprising: emulsionpolymerizing first-stage monomers in an aqueous carrier to produce afirst-stage copolymer comprising water dispersing groups, wherein thefirst-stage monomers include greater than 3% by weight, based on anentire weight of the first-stage monomers, of step-growth-functionalmonomers comprising carboxylic acid-functional groups, anhydridesthereof, salts thereof, or combinations thereof; alcohol-functionalgroups; amine-functional group, or combinations thereof; and emulsionpolymerizing second-stage monomers in the presence of the first-stagecopolymer to form a second-stage copolymer, wherein the second-stagecopolymer is chemically different from the first-stage copolymer, andwherein the second-stage copolymer comprises a curing group comprisingat least one functional group comprising an oxirane group, an isocyanategroup, an azlactone group, an oxazoline group, a cyclocarbonate group,or a combination thereof; wherein the coating composition issubstantially free of structural units derived from each of(meth)acrylamide-type monomers, bisphenol A, bisphenol F, and bisphenolS; and wherein the coating composition, when cured, has a glasstransition temperature of greater than about 35° C.; and wherein thefirst-stage copolymers include a sufficient amount of water-dispersinggroups so that the first-stage copolymer can function as a polymericsurfactant to facilitate emulsion polymerization of the second-stagemonomers.
 45. The coating composition of claim 44, wherein thefirst-stage monomers comprise one or more polymerizable surfactantmonomers.
 46. The coating composition of claim 44, wherein emulsionpolymerizing the first-stage monomers is performed without the use ofany polymerizable or non-polymerizable surfactants.
 47. The coatingcomposition of claim 44, wherein after curing, the coating composition,without an external crosslinker, withstands more than 100 double rubswhen tested according to the Solvent Resistance Test described herein.